overflow valve constantly leaking

I live in a 1928 bungalow style house and have an old furnace, converted to gas, forced hot water. the radiators are all on first floor....NOTHING on second floor. The gas company put an overflow valve next to my furnace when I had a pipe leak....it drips constantly (a bucket a day)...when talking to people they ask about my expansion tank.....THERE IS NONE....honest.......there never was an overflow valve nor was there an expansion tank....but how can this be?
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John O'Keefe wrote:

It's a boiler, not furnace (just so you know). Overflow ...means pressure relief, probably.
In 1928, it was common to hide the exp tank in an attic space. Whether it's hidden away or there really is none, you need one. Today's exp tanks are quite small and can added right near the boiler.
Jim
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Are the tanks expensive? I have searched the attic and followed every pipe....more than once....there is no tank. Have you ever heard of a system where there was never a tank nor an overflow valve?

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John O'Keefe wrote:

http://www.zurn.com/pages/catalog.asp?ProductGroupID &OperationID Look at Model HXT
Jim
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wrote:

There may have been a tank in the attic that has been removed? It was also once common to connect the boiler to a high mounted toilet tank that would take the expansion and drop it to the overflow when necessary. I've found this at times. When the toilet got replaced with a modern unit they just capped the pipe and now there's no expansion provision. It wouldn't be hard to add one.
Dan
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wrote:

There may be an expansion tank hidden by later construction. If so, it is full and needs to be drained. If you don not have an expansion tank, one should be added. They make them to fit between floor joists above the boiler area.
BB
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I am not a heating expert, but I imagine what you call an overflow valve is a pressure relief valve, water expands when heated, and without an expansion tank, just enough goes out the relief to (hopefully) keep the pressure from going too high. There is a forum called "The Wall" on http://www.heatinghelp.com/ and they have a "Find a Pro" link there too if you do not know who could help you locally.
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